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Subject: Re: [Boost-users] [Geometry] 3D Oriented Bounding Box
From: Simonson, Lucanus J (lucanus.j.simonson_at_[hidden])
Date: 2011-12-15 16:07:03


Jeremy Coulon wrote:
Le 14/12/2011 19:37, Barend Gehrels a écrit :
>> Yes, I can tell you that alas this is not possible with the current
>> version. OBB's are not yet supported. Besides that, 3D intersections
>> (besides trivial ones) are far from implemented...

>Another little question. When you say 3D intersections are not
>implemented, does it mean that
>a) it would not even compile
>b) it compiles but gives wrong results
>c) it gives correct results but is not optimized for 3D ?

The answer is (a) for the non-trivial intersections, but there seems to be a misunderstanding about the nature of 3D intersections. 3D solid modeling/meshing/graphics algorithms are not achieved by putting a template parameter for dimensionality on the 2D algorithm, passing 3 and getting the 3D algorithm. The algorithms for 3D intersections on 3D solids represented by a surface mesh, for example, are completely different than the algorithms for 2D intersections of polygons. They are less efficient (quadratic versus near-linear wrt. vertex count) and much harder to make numerically robust because of the higher order arithmetic involved. A 3D solid modeling library is an order of magnitude larger in scope than a 2D geometry library. What is meant by "non-trival" in this context is multiple man years of work, up to a decade or more to be competitive with the closed source offerings in terms of features, reliability and performance.

Regards,
Luke


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